The present invention relates to the field of tank cleaning, and more particularly to an improved system and method for positively guiding a tank-cleaning device or the like around the inside of a tank.
Material handling units, such as holding tanks or the like, are used in a wide range of industries, such as pulp and paper industries, chemical industries, mining and refining industries and steel industries. One problem that exists with the use of such holding tanks is that, over time, the liquid in the holding tank can no longer dissolve solids therein, and the solids fall out or are precipitated and load the bottom of the tank. Such fallout reduces tank capacity, stop pumps, and, in some instances, locks in valuable capital costs of material. Often, the buildup of solids in the tank occurs well before management personnel become aware of the problem, thereby resulting in tons of precipitated solids collected in the bottom of the tank. Tanks vary in size and shape and, in some instances, can be at least 40 feet high by 100 feet in diameter. Obviously, due to the nature holding tanks, removal of solids or sludge from the bottom thereof is not simple task. However, due to the aforementioned disadvantages of sludge buildup, such tanks must often be periodically cleaned.
One method and device which can be used to remove solids or sludge from the bottom of a tank is disclosed in U.S. Pat. No. 5,253,812, issued to the instant inventor. Such devices are designed to be placed in a tank on top of the solid deposit or sludge and include cutting wheels for breaking down and facilitating removal of the sludge from the tanks. While this and similar cleaning devices have proved to be useful in removing sludge from tanks, they require hydraulic motors and propellers for movement around the inside of the tank. As explained in the '812 patent, by generating both vertical and horizontal propulsion, it is possible to cause the cleaning device to move randomly around the bottom of the tank to facilitate cleaning thereof. However, in some instances, the hydraulic motors and propellers do not provide sufficient control of the movement of the cleaning device within the tank. Thus, a need exists for a method and device which enables improved control of the directional movement of a cleaning device, or the like, while operating within a tank.